Process for the preparation of chlorine dioxide



Jan. 17, 1956 KESTlNG 2,731,325

PROCESS FOR THE PREPARATIONOF CHLORINE DIOXIDE Filed Jan. 9, 1952 2 6 meat Va 5412/ 67'0124 E Bic 6P T6625 United States Patent PROCESS FOR THE PREPARATION OF CHLORINE DIQXIDE Edelbert E. Kesting, Munich, Germany Application January 9, 1952, Serial No. 265,662 Claims priority, application Germany June 5, 1951 1 Claim. (Cl. 23-452) This invention is directed to a new and improved method for the preparation of metal chlorates, such as sodium chlorate, and to new and improved apparatus for carrying out that method.

In the preparation of chlorine dioxide by reacting a chlorate and an acid, preferably by using sodium chlorate and hydrochloric acid, it has been suggested to feed the mixed solution of sodium chloride (table salt) and sodium chlorate which is discharged from the chlorine dioxide production apparatus, i. e. the so-called reaction apparatus, to a chlorate electrolysis vessel in order thereby to reconvert the table salt, either in whole or in part, back again into sodium chlorate. The sodium chlorate solution formed is recycled into the reaction apparatus, therein again reacted with hydrochloric acid, and then again brought to the electrolysis, the process being then repeated.

The quantity of solution discharging from the reaction apparatus is larger than the quantity of chlorate solution flowing into this apparatus, inasmuch as it is increased by the water which enters with the hydrochloric acid, as well as by the water which has formed during the chemical reaction. Moreover, in processes wherein the heating of the solution is effected in the reaction apparatus by the direct blowing-in of steam, it is still further increased by the water resulting from the condensation of this steam.

It is, therefore, necessary to remove sufiicient water so that the volume of the solution which discharges per unit of time from the electrolysis is the same as the quantity of chlorate solution fed, during the same period of time, into the reaction apparatus. Obviously, this may be done by evaporation of the water. For this there is needed an evaporator, which introduces additional difliculties of a considerable nature, owing to the corrosive nature of the solution on the structural material employed for the apparatus. in addition to this heat is needed to carry out the evaporation.

In the electrolytic cell only a part of the current fed is used for the electrolysis proper. A certain part of the current is converted into heat, as a result of which the temperature of the electrolyte is increased. Inasmuch as this is permissible only up to a certain degree, however, it is necessary to employ cooling during the electrolysis. This is effected in the known manner by the use of cooling coils located in the electrolysis vessel, through which coils the cooling agent flows. Such cooling coils meet the requirements only very inadequately, inasmuch as they are formed either of corrosion-resistant material, such, for instance, as glass, porcelain or the like, or, it formed of metal, they must be provided with an outer rubber covering. In both cases the heat transfer from the cooling agent to the electrolyte liquid is poor. The cooling coils may also be formed of metal and be connected as cathodes, but this arrangement, however, possesses certain inherent structural disadvantages.

Regardless of how the cooler device is constructed, and regardless of whether it is placed in the electrolytic cell,

or in a supply vessel located in a recycling line, the heat to be removed must always be transferred to the cooling agent and led away from the apparatus by the use of the said agent.

One of the objects of the present invention is to use the heat which must be led away during the electrolysis for concentrating the reaction solution. This is carried out in that the discharged reaction solution, which is to be concentrated, is fed to a storage vessel which is connected in a cycle with the electrolytic cell and an evaporation cooler.

The electrolyte circulating in this cycle is heated in the cell, passes via the storage vessel into the evaporation cooler, is cooled therein, and is then returned back into the cell, whereupon the cycle is repeated. In the evaporation cooler 21 small part of the electrolyte is evaporated Without any external addition of heat, the temperature thus decreasing. The evaporation cooler can be constructed in a known manner as a vacuum cooler, or it may be formed as a tower in which the solution trickles down and is partly evaporated by a countercurrent fiow of air, thus cooling it.

The annexed drawing shows, diagrammatically, one embodiment of an installation constructed in accordance with my invention.

in this drawing, the electrolysis vessel is represented by the numeral 1. Into the electrolysis vessel 1 there passes a conduit 2, through which electrolyte is admitted in the form, for instance, of a mixed solution of sodium chloride and sodium chlorate, conduit 2 leads from an evaporation cooler 3, which is filled with Raschig rings, and which is provided at its bottom with a conduit or pipeline 4 for the admission of air. At the top of the evaporation cooler 3, there is provided a conduit 5 for admitting to this evaporation cooler the solution which is discharged thereinto. The evaporator 3 is furthermore provided, at its top, with a discharge conduit 6 for withdrawing the air-water vapor mixture. Conduit 5 leads from a storage receptacle 7, into the top of which vessel there leads an overflow conduit 8 leading from the elecrolysis vessel 1. There is furthermore provided a conduit 9 for the admission of spent liquid to the storage receptacle. A pump 16 is located in pipeline 5. The conduit 9 proceeds from reaction apparatus 11, to which strengthened liquor from storage receptacle 7, is pumped by pump 12 and pipe 13.

Electrolyte continuously flows to the electrolyzing vessel 1 through the conduit or pipeline 2, this electrolyte then discharging through line 8 into the storage vessel. From the storage vessel 7 the liquid passes, via pump 10 and pipeline 5, into the evaporation cooler 3. In this evaporation cooler 3 the liquid, heated for example to about 45 C., is partly evaporated or volatilized without any addition of heat by the fine distribution and admission of air. It is thus cooled, for example, to 40 C. The cooled, non-evaporated liquid passes, via pipeline or conduit 2, into the electrolyzing vessel 1 with a temperature, for instance, of about 40 C. Here it is again heated to 45 C., and the cycle is then repeated.

Under ordinary operating conditions and with a proper adjustment of the pump 10 relative to the air stream or vacuum acting on the evaporator, the heat produced in the electrolysis is just sullicient to support evaporation in the evaporator of the excess water introduced into the reaction solution in the reaction stage by the addition of HCl solution and condensation of steam. However, if the quantity of liquid is not sufiicient it can be increased to the correct and necessary quantity by the addition of water to the circulating system for example via conduit 9. On the other hand, if the quantity of liquid is too large, the missing quantity of heat can be supplied by means of a suitable disposed heat exchanger.

The method herein described therefore has the advantage that an evaporator, and the necessary heat to operate the evaporator, are saved on the side of the reaction apparatus; while, on the electrolysis side, the expense of a cooling apparatus and the cooling agent are eliminated.

Various changes and modifications may be made in my improved method and in the appaartus for carrying out that method, certain preferred forms of which have been herein described, without departing from the spirt or scope of the invention. To the extent that they are included within the purview of the appended claim, they are to be regarded as within the scope of my invention.

I claim:

A process of electrolytically manufacturing chlorine dioxide, including the steps of reacting an aqueous chlorate salt solution and hydrochloric acid so as to liberate chlorine dioxide in a reaction zone, discharging and storing in a storing vessel the weakened liquor containing said chlorate salt and the corresponding chloride, regenerating said weakened liquor, said regeneration including the steps of passing said liquor into an electrolysis chamber, electrolyzing therein said liquor, whereby to transform at least part of said chloride into a chlorate, cyclically pump.- ing said liquor in a first pumping cycle between said re action zone and the storing vessel and cyclically and independently of said first pumping cycle, lowering the temperature of said liquor by evaporation therefrom of a portion of the water acting as a solvent for said chloride and said chlorate, during the passage of said liquor from the storage vessel into the electrolysis chamber and re turning the regenerated liquor from the electrolysis chamber into the storage tank.

References Cited in the file of this patent UNITED STATES PATENTS 1,847,435 Low Mar. 1, 1932 1,917,657 MacChesney July 11, 1933 2,484,402 Day et al. Oct. 11, 1949 

